February 2014


Period: From February 2014      Issued on 12.02.2014 using data to the end of January

Summary

January saw a continuation of the exceptionally stormy and wet weather of late December. It was the wettest January on record in many parts of the UK, and for much of southern England, the rainfall for January and December combined was the highest for any two-month period since 1910. As a consequence, January river flows and groundwater levels were exceptional. Rainfall projections favour a wet February, and the month so far has been very wet in southern England. All sources of evidence suggest February river flows and groundwater levels will continue to be substantially above-normal and are likely to be exceptionally high in some areas of southern and central Britain. The outlook for February to April suggests notably high flows and groundwater levels are very likely to persist, implying an elevated risk of further river flow and groundwater flooding over the next three months. In areas vulnerable to groundwater flooding, the risk is likely to continue well into late spring.  Up-to-date flood warnings are available from the websites of the Environment Agency, Natural Resources Wales and Scottish Environment Protection Agency.

Rainfall

During February, the balance of probabilities suggests a continuation of the very unsettled weather experienced so far this winter, with above-average rainfall most probable. For February-March-April, predictions for rainfall are very uncertain and largely indistinguishable from climatology. The probability that UK precipitation for February-March-April will fall into the wettest of five equal classes is between 20 and 25% and the probability of falling into the driest of five equal classes is between 15 and 20% (the 1981-2010 probability for each of these classes is 20%).

River flows

January river flows were exceptional across southern Britain (new records for January average river flows were widespread) and notably high river flows were also registered across many northern areas, with below-normal flows confined to a few catchments in the far north of Scotland. The one-month ahead outlook suggests a continuation of above-normal river flows across much of the UK, with a high likelihood of notably high or exceptional flows in central and southern areas. The three-month ahead outlook is strongly indicative of above-normal flows persisting, with a high likelihood of notably high or exceptional river flows over this period. Given the persistent rainfall since mid-December, catchments are saturated and highly sensitive to further rainfall across much of the UK. There is therefore a very high risk of further river flow flooding in February, particularly in southern and central England, and flood risk will remain elevated over the next three months.

Groundwater

January groundwater levels were above normal across all major aquifers, with the exception of parts of the eastern Chalk. Levels were exceptionally high across the southern Chalk, with a number of new maximum groundwater levels established, and in the Permo-Triassic sandstone of the northwest. The one-month outlook indicates that notably high levels will persist in most aquifers, although normal levels are likely in the eastern Chalk, with below normal levels in East Yorkshire. Exceptional levels are possible in parts of the southern Chalk and in the Permo-Triassic of the northwest, even if low rainfall amounts are received – however, given the wet start to February this is unlikely. The three-month outlook indicates a continuation of the current situation. Levels in the southern Chalk are likely to be notably high - an elevated risk of groundwater flooding in vulnerable areas will continue until April at least, although persistence of flood risk into late spring is highly likely (as occurred in the winter of 2000/2001). The long-term outlook suggests it could be many months before a return to normal levels.